Suppress Safari promise rejections.

Currently Webkit implements createImageBitmap() but returns a promise
rejection.

Note that once Webkit implements createImageBitmap() correctly these
changes should be removed.

src/shared/utils/Browser.ts

@@ -8,6 +8,7 @@ const userAgent = (isNode) ? 'node' : navigator.userAgent;
 const platform = (isNode) ? 'node' : navigator.platform;
 
 export const isFirefox = !!~userAgent.indexOf('Firefox');
+export const isSafari = !!~userAgent.indexOf('Safari');
 export const isMSIE = !!~userAgent.indexOf('MSIE') || !!~userAgent.indexOf('Trident');
 
 // Find the users platform. We use this to interpret the meta key